DE102023202219A1 - Improved indigo-based dye - Google Patents

Abstract

The invention relates to an agent and a method for coloring keratin-containing fibers, in particular human hair, using a plant powder producing indigo or indirubin, isatin and cysteine.

Description

The invention relates to an agent and a method for coloring keratin-containing fibers, in particular human hair, using a plant powder producing indigo or indirubin in combination with isatin and cysteine.

The desire to change one's hair color is a great need of many consumers. To satisfy this need, the cosmetics industry offers a diverse range of products. Hair dyes that achieve particularly long-lasting coloring with high coverage are usually oxidation dyes. These use oxidizing agents that can damage the hair structure. Certain cationic direct azo dyes are also able to enable hair color changes with excellent fastness properties. However, the azo dyes mentioned are synthetic dyes.

A growing number of consumers are demanding hair dyes and hair coloring processes based on natural dyes, even though these products and processes are often inferior to the aforementioned products and processes in terms of authenticity, coverage and color variety.

In addition to dyeing hair with henna, which is obtained from the plant Lawsonia inermis, the dyeing of hair with plants from which indigo or indirubin can be produced has also been known for a long time.

State of the art

There has been no lack of efforts in the state of the art to improve the coloring of keratin fibers, especially human hair, with indigo.

The addition of natural dyes to oxidative hair dyes is also popular. The dye cream is mixed with an aqueous preparation containing hydrogen peroxide shortly before application to the hair. The dye cream mainly contains oxidation dye precursors, for example toluene-2,5-diamine sulfate, 4-chlororesorcinol, 2-methylresorcinol, 2-amino-4-hydroxyethyl-aminoanisole sulfate, 4-amino-2-hydroxytoluene, 4-amino-m-cresol and m-aminophenol; the natural dye content is only used for nuance. The coloring achieved in this way is essentially a standard oxidative coloring with high fastness properties. The problem of the lack of adhesion of the natural dye plays a minor role in such products. WO2015082482A1 A process for oxidative hair coloring is known in which powdered plant parts from plants that produce indigo are used in the presence of hydrogen peroxide, but no oxidation dye precursors. In any case, the hair is damaged by the oxidizing agent.

When dyeing keratin fibers with indigo, without creating special conditions such as pre- or post-treatment or adding certain active ingredients, a color shift from an initial turquoise-blue tone to a redder and darker shade, creating a purple color impression, could be observed from a concentration of 2% by weight of indigo-producing plant powder in water approximately two weeks after dyeing.

Out of DE4211450A1 Non-oxidative hair dyes are known which contain isatin in combination with at least one amino acid, for example cysteine, or a water-soluble oligopeptide composed of 2 to 9 amino acids in an aqueous carrier.

Task

One object was to provide agents and methods for coloring keratin-containing fibers, in particular human hair, using plants that produce indigo or indirubin, with which a wider range of colorations can be achieved. In particular, colorations beyond the typical indigo blue, in particular colorations with a shift into warmer color ranges, should be provided. A further object of the present invention was to provide agents and methods for coloring keratin-containing fibers, in particular human hair, using plants that produce indigo or indirubin, with which the final color result is obtained as soon as possible after completion of the actual coloring process.

Surprisingly, it was found that with the dyes described in the patent claims and with the dyeing process described in the patent claims using plants that produce indigo or indirubin in combination with cysteine and isatin, an intense magenta hair color could be achieved immediately after the dyeing process. It was also possible to achieve the final color result shortly after the actual dyeing process had been completed and - unlike what is often typical for dyeing with indigo - this color result did not change in the days after the dyeing process had been completed. Neither the initial turquoise-blue color tone characteristic of indigo nor the final purple tone were formed on the hair fiber.

A first subject matter of the present invention is therefore an agent for the non-oxidative coloring of keratin fibers, in particular human hair, containing water, cysteine, isatin and at least one indigo or indirubin-producing plant powder i), wherein the agent has a pH of 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, in each case measured at 20°C.

The terms “colorant according to the invention” and coloring composition (A) are used synonymously in the present application.

Unless otherwise stated, room temperature means a temperature of 20°C.

All pH values refer to measurements at 20°C.

• - Indigofera, insbesondere Indigofera tinctoria, Indigo suffruticosa, Indigofera articulata, Indigofera arrecta, Indigofera heterantha „Gerardiana“, Indigofera argentea oder Indigofera longiracemosa;
• - Isatis, insbesondere Isatis tinctoria (Färberwaid);
• - Persicaria, insbesondere Persicaria tinctoria (Färber-Knöterich);
• - Wrightia, insbesondere Wrightia tinctoria;
• - Calanthe, insbesondere Calanthe veratrifolia; und
• - Baphicacanthus cusia, synonym Strobilanthes cusia.

Preferred dyes according to the invention are characterized in that the indigo or indirubin producing plant(s) is/are selected from at least one species of the following genera:

• - Indigofera, in particular Indigofera tinctoria, Indigo suffruticosa, Indigofera articulata, Indigofera arrecta, Indigofera heterantha “Gerardiana”, Indigofera argentea or Indigofera longiracemosa;
• - Isatis, especially Isatis tinctoria (woad);
• - Persicaria, especially Persicaria tinctoria (dyer's knotweed);
• - Wrightia, especially Wrightia tinctoria;
• - Calanthe, especially Calanthe veratrifolia; and
• - Baphicacanthus cusia, synonym Strobilanthes cusia.

Particularly preferred plants producing indigo or indirubin are selected from the genus Indigofera and in particular from Indigofera tinctoria.

The plants of the genera and species mentioned above contain no or only small amounts of indigo and indirubin. Instead, the plants contain the compound indican, a precursor of indigo and indirubin. The parts of the plant genera and species mentioned above that are rich in indican and also contain indigo or indirubin are the leaves of these plants. For use as a dye for keratin fibers, the plant leaves of the plant genera and species mentioned above are dried and ground and used as plant powder.

Plant powders preferred according to the invention have a particle size of less than 500 µm, particularly preferably in the range of 120 µm - 200 µm, extremely preferably in the range of 150 µm - 180 µm. Other plant powders preferred according to the invention have a bulk density in the range of 0.20 - 0.60 g/cm ³ , particularly preferably in the range of 0.25 - 0.40 g/cm ³ . Other plant powders preferred according to the invention have, based on their weight, a moisture content of less than 10% by weight, preferably 0.1 - 6.0% by weight, particularly preferably 0.2 - 3.0% by weight. The moisture content is determined after 3 hours of drying at 105°C.

It is preferred according to the invention that the powder of the indigo or indirubin producing plant, based on its weight, consists of at least 50 wt.%, preferably at least 80 wt.%, particularly preferably more than 80 - 100 wt.%, of the leaves of the plant. Further colorants preferred according to the invention are characterized in that the powder of the indigo or indirubin producing plant has a particle size of less than 500 µm, particularly preferably in the range of 120 µm - 200 µm, extremely preferably in the range of 150 µm - 180 µm, and also a bulk density in Range of 0.20 - 0.60 g/cm ³ , particularly preferably in the range of 0.25 - 0.40 g/cm ³ and, based on its weight, a moisture content of less than 10 wt.%, preferably from 0.1 - 6.0 wt.%, particularly preferably from 0.2 - 3.0 wt.%.

Further colorants preferred according to the invention are characterized in that the powder of the indigo or indirubin producing plant contains the compound indican in an amount of 2 - 5 wt.%, preferably 2.5 - 4.5 wt.%, particularly preferably 3 - 4.1 wt.%, based on the weight of the powder.

Further colorants preferred according to the invention are characterized in that at least one indigo or indirubin-producing plant powder i) is contained in a total amount of 1-80% by weight, preferably 2-50% by weight, particularly preferably 3-25% by weight, extremely preferably 4-15% by weight, further extremely preferably 5-10% by weight, further extremely preferably 6-7% by weight, based on the weight of the agent.

Further colorants preferred according to the invention are characterized in that powdered leaves of Indigofera tinctoria are contained in an amount of 1-80% by weight, preferably 2-50% by weight, particularly preferably 3-25% by weight, extremely preferably 4-15% by weight, further extremely preferably 5-10% by weight, further extremely preferably 6-7% by weight, based on the weight of the agent.

Colorants preferred according to the invention are characterized in that cysteine is contained in an amount of 0.1 - 5.0 wt.%, preferably 0.5 - 3.0 wt.%, particularly preferably 0.8 - 2.0 wt.%, extremely preferably 1.0 - 1.5 wt.%, based on the weight of the agent.

Cysteine as a chiral amino acid has a stereogenic center and can occur in a mirror-image form, namely in the form of L-cysteine and D-cysteine. Both L-cysteine and D-cysteine as well as mixtures thereof are encompassed by the present invention. Within the scope of the present invention, both possible enantiomers can therefore be used equally as a specific compound or mixtures thereof, in particular as racemates. However, it is particularly advantageous according to the invention to use the naturally occurring isomer form, here L-cysteine.

Colorants which are particularly preferred according to the invention are characterized in that L-cysteine is contained in an amount of 0.1 - 5.0% by weight, preferably 0.5 - 3.0% by weight, particularly preferably 0.8 - 2.0% by weight, extremely preferably 1.0 - 1.5% by weight, based on the weight of the agent.

An aqueous solution of cysteine reacts acidically. A 1% by weight solution of L-cysteine in deionized water has a pH of 6.49, measured at 20°C. Cysteine is therefore not an alkalizing agent.

Powders from the leaves of Indigofera tinctoria that are preferably used according to the invention react approximately neutrally in aqueous dispersion, with slight deviations between a slightly acidic and a slightly alkaline pH range. A 5% by weight dispersion of ground leaves of Indigofera tinctoria in deionized water has a pH of 6.6 to 7.4, preferably 6.8 to 7.2, particularly preferably 6.9 to 7.1, in each case measured at 20°C.

Further colorants preferred according to the invention are characterized in that isatin is contained in an amount of 0.01 - 1.0 wt.%, preferably 0.05 - 0.5 wt.%, particularly preferably 0.08 - 0.3 wt.%, extremely preferably 0.1 - 0.2 wt.%, based on the weight of the agent.

For the effects according to the invention, it has proven particularly advantageous if cysteine is contained in a molar excess to isatin.

Further preferred colorants according to the invention are therefore characterized in that cysteine is contained in molar excess to isatin.

Particularly preferred colorants according to the invention are characterized in that the molar ratio of cysteine to isatin is 1.5 to 20, preferably 3 to 18, particularly preferably 5 to 15, extremely preferably 10 to 13.

The dyes according to the invention also contain water. The water serves to disperse the plant powder and to dissolve the indican contained therein and make it available for reaction to form indigo and indirubin.

Colorants preferred according to the invention are characterized in that water is contained in an amount of 19.9 - 95.0 wt.%, preferably 30.0 - 90.0 wt.%, particularly preferably 50.0 - 88.0 wt.%, extremely preferably 60.0 - 85.0 wt.%, based on the weight of the agent.

The colorants according to the invention have a pH of 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, in each case measured at 20°C.

A dispersion of 5% by weight of ground leaves of Indigofera tinctoria in deionised water, in which 1% by weight of L-cysteine and 0.1% by weight of isatin are also dissolved, has a pH of 7.4, measured at 20°C, the quantities referring to the weight of the total aqueous preparation.

Very good dyeing results are already achieved in the pH range around the pH of 7.0 to 7.4, i.e. in particular from 5.0 to 8.0, preferably from 6.7 to less than 7.5, which spontaneously occurs in the mixture of ground leaves of Indigofera tinctoria, cysteine and isatin in deionized water, each measured at 20°C.

In a preferred embodiment of the dyeing process according to the invention, the desired pH of the aqueous dyeing composition (A) is adjusted using an acid or a base. Preferred acids are selected from citric acid, lactic acid, gluconic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, galactaric acid (mucous acid), tartaric acid, malic acid, sulfuric acid and phosphoric acid, and mixtures of these acids. Preferred bases are sodium hydroxide, potassium hydroxide, arginine, lysine, monoethanolamine, triethanolamine, 2-amino-2-methylpropan-1-ol, and mixtures of these bases.

In a further preferred embodiment of the dyeing process according to the invention, the desired pH of the aqueous dyeing composition (A) is adjusted with the aid of a buffer system selected from a mixture of a medium-strong or weak acid with its conjugated or corresponding base (or the respective salt) and a mixture of a medium-strong or weak base with its conjugated or corresponding acid.

• - Ammoniak/Ammoniumsalz-Mischungen, wobei das Ammoniumsalz bevorzugt ausgewählt ist aus Ammoniumchlorid, Ammoniumbromid, Ammoniumhydrogensulfat, Ammoniumsulfat, Ammoniumdihydrogenphosphat, Diammoniumhydrogenphosphat, Ammoniumphosphat, Ammoniumbicarbonat, Ammoniumcarbonat, Ammoniumnitrat, Ammoniumacetat, Ammoniumglycolat, Ammoniumgluconat, Ammoniumtartrat. Ammoniumlactat, sowie Mischungen dieser Ammoniumsalze, besonders bevorzugt ausgewählt aus Ammoniumchlorid, Ammoniumhydrogensulfat, Ammoniumsulfat, Ammoniumdihydrogenphosphat, Diammoniumhydrogenphosphat, Ammoniumphosphat, Ammoniumbicarbonat und Ammoniumcarbonat, außerordentlich bevorzugt ausgewählt aus Ammoniumchlorid,
• - Mischungen aus Hydrogenphosphat und Dihydrogenphosphat, insbesondere den Alkalimetallsalzen von Hydrogenphosphat und Dihydrogenphosphat, besonders bevorzugt den Natriumsalzen oder/und den Kaliumsalzen von Hydrogenphosphat und Dihydrogenphosphat,
• - Mischungen aus Alkalimetallhydrogencarbonat mit Alkalimetallcarbonat, insbesondere Mischungen aus Natrium- oder Kaliumhydrogencarbonat mit Natrium- oder Kaliumcarbonat,
• - Mischungen aus Citronensäure und ihren Salzen, insbesondere den Alkalimetallcitraten, insbesondere den Natriumsalzen, insbesondere Trinatriumcitrat,
• - Mischungen aus Weinsäure und ihren Salzen, insbesondere den Alkalimetalltartraten, insbesondere den Kaliumsalzen, insbesondere Kaliumhydrogentartrat,
• - Mischungen aus Phthalsäure und ihren Salzen, insbesondere den Kaliumsalzen, insbesondere Kaliumhydrogenphthalat,
• - Mischungen aus Milchsäure und ihren Salzen, insbesondere Milchsäure/Natriumlactat-Mischungen,
• - Mischungen aus Gluconsäure und ihren Salzen, insbesondere Gluconsäure/Natriumgluconat-Mischungen,
• - Mischungen aus Bernsteinsäure und ihren Salzen, insbesondere den Natriumsalzen, insbesondere Natriumhydrogensuccinat und Dinatriumsuccinat, sowie
• - Mischungen aus Äpfelsäure und ihren Salzen, insbesondere den Natriumsalzen, insbesondere Natriumhydrogenmalat und Dinatriummalat, sowie
• - Ammoniak/Ammoniumsalz-Mischungen, wobei das Ammoniumsalz bevorzugt ausgewählt ist aus Ammoniumchlorid, Ammoniumbromid, Ammoniumhydrogensulfat, Ammoniumsulfat, Ammoniumdihydrogenphosphat, Diammoniumhydrogenphosphat, Ammoniumphosphat, Ammoniumbicarbonat, Ammoniumcarbonat, Ammoniumnitrat, Ammoniumacetat, Ammoniumglycolat, Ammoniumgluconat, Ammoniumtartrat. Ammoniumlactat, sowie Mischungen dieser Ammoniumsalze, besonders bevorzugt ausgewählt aus Ammoniumchlorid, Ammoniumhydrogensulfat, Ammoniumsulfat, Ammoniumdihydrogenphosphat, Diammoniumhydrogenphosphat, Ammoniumphosphat, Ammoniumbicarbonat und Ammoniumcarbonat, außerordentlich bevorzugt ausgewählt aus Ammoniumchlorid.

According to the invention, preferred corresponding acid-base pairs are those which stabilize the aqueous dye composition (A) used according to the invention in the pH range from 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, each measured at 20°C. Particularly preferred buffer systems according to the invention for the aqueous dye composition (A) used according to the invention are selected from

• - ammonia/ammonium salt mixtures, wherein the ammonium salt is preferably selected from ammonium chloride, ammonium bromide, ammonium hydrogen sulfate, ammonium sulfate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium bicarbonate, ammonium carbonate, ammonium nitrate, ammonium acetate, ammonium glycolate, ammonium gluconate, ammonium tartrate, ammonium lactate, and mixtures of these ammonium salts, particularly preferably selected from ammonium chloride, ammonium hydrogen sulfate, ammonium sulfate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium bicarbonate and ammonium carbonate, extremely preferably selected from ammonium chloride,
• - mixtures of hydrogen phosphate and dihydrogen phosphate, in particular the alkali metal salts of hydrogen phosphate and dihydrogen phosphate, particularly preferably the sodium salts and/or the potassium salts of hydrogen phosphate and dihydrogen phosphate,
• - mixtures of alkali metal hydrogen carbonate with alkali metal carbonate, in particular mixtures of sodium or potassium hydrogen carbonate with sodium or potassium carbonate,
• - mixtures of citric acid and its salts, in particular the alkali metal citrates, in particular the sodium salts, in particular trisodium citrate,
• - mixtures of tartaric acid and its salts, in particular alkali metal tartrates, in particular potassium salts, in particular potassium hydrogen tartrate,
• - Mixtures of phthalic acid and its salts, in particular potassium salts, in particular potassium hydrogen phthalate,
• - mixtures of lactic acid and its salts, in particular lactic acid/sodium lactate mixtures,
• - mixtures of gluconic acid and its salts, in particular gluconic acid/sodium gluconate mixtures,
• - mixtures of succinic acid and its salts, in particular the sodium salts, in particular sodium hydrogen succinate and disodium succinate, and
• - Mixtures of malic acid and its salts, in particular the sodium salts, in particular sodium hydrogen malate and disodium malate, and
• - Ammonia/ammonium salt mixtures, wherein the ammonium salt is preferably selected from ammonium chloride, ammonium bromide, ammonium hydrogen sulfate, ammonium sulfate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium bicarbonate, ammonium carbonate, ammonium nitrate, ammonium acetate, ammonium glycolate, ammonium gluconate, ammonium tartrate, ammonium lactate, and mixtures of these ammonium salts, particularly preferably selected from ammonium chloride, ammonium hydrogen sulfate, ammonium sulfate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium bicarbonate and ammonium carbonate, extremely preferably selected from ammonium chloride.

Other buffer systems, e.g. acetic acid/sodium acetate, are also suitable in principle according to the invention. However, due to the vinegar smell, such a buffer is not acceptable for the manufacture of a cosmetic market product.

For varying the pH value, further preferred colorants and coloring processes according to the invention are characterized in that the aqueous coloring composition (A) contains a buffer system for pH adjustment, selected from a mixture of a medium-strong or weak acid or base with its conjugated or corresponding base or corresponding acid.

Further dyeing processes preferred according to the invention are characterized in that the aqueous dyeing composition (A) contains a buffer system selected from an ammonia/ammonium salt mixture for pH adjustment in the basic range. Preferred ammonium salts which buffer the strongly basic pH of the aqueous ammonia solution to a less basic pH are selected from ammonium chloride, ammonium bromide, ammonium hydrogen sulfate, ammonium sulfate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium bicarbonate, ammonium carbonate, ammonium nitrate, ammonium acetate, ammonium glycolate, ammonium gluconate, ammonium tartrate, ammonium lactate, and mixtures of these ammonium salts. Ammonium chloride, ammonium hydrogen sulfate, ammonium sulfate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium bicarbonate and ammonium carbonate are particularly preferred. Ammonium chloride is particularly preferred.

In principle, other buffer systems are also suitable.

Further dyeing processes preferred according to the invention are characterized in that the aqueous dyeing composition (A) contains a buffer system selected from a hydrogen phosphate salt/dihydrogen phosphate salt mixture for pH adjustment. Suitable salts are the sodium salts and the potassium salts of hydrogen phosphate and dihydrogen phosphate. With hydrogen phosphate salt/dihydrogen phosphate salt mixtures, pH values in the range from 7.1 to about 8.2 can be adjusted.

For higher pH values up to pH < 10.0, mixtures of sodium or potassium hydrogen carbonate with sodium or potassium carbonate are suitable. Further dyeing processes preferred according to the invention are therefore characterized in that the aqueous dyeing composition (A) contains a buffer system selected from a mixture of sodium or potassium hydrogen carbonate with sodium or potassium carbonate for pH adjustment. Suitable salts are the sodium salts and the potassium salts of hydrogen carbonate and carbonate. With hydrogen carbonate salt/carbonate salt mixtures, pH values in the range from about 9.0 to < 10.0 can be adjusted.

The specialist can find out the appropriate weights of buffer salts to set the desired pH value from the relevant manuals.

Preferred dyeing agents and dyeing processes according to the invention are further characterized in that no hydrogen peroxide is used in them.

Preferred colorants and coloring processes according to the invention are further characterized in that no ions and compounds of metals other than alkali metals and alkaline earth metals are used in them. The content of metal ions other than alkali metal ions and alkaline earth metal ions, which are contained in trace amounts in the water used, e.g. in tap water or city water, is not taken into account here. Tap water can contain an average of 2 mg of copper ions per liter, i.e. about 0.0002% by weight of copper ions. The maximum concentration of metal ions other than alkali metal ions and alkaline earth metal ions in preferred colorants according to the invention is 0.00001 - 0.002% by weight, preferably 0.0001 to 0.001% by weight, particularly preferably a maximum of 0.0007% by weight, in each case based on the colorant.

If salts are to be present, the salts of alkali metals and alkaline earth metals, in particular the salts of sodium, potassium and magnesium, preferably the salts of sodium and potassium, are suitable according to the invention.

According to the invention, salts and compounds of aluminum, transition metals and lanthanides are particularly undesirable. The metals mentioned in their elemental form are also not used in the colorants and coloring processes according to the invention.

In conventional dyes and dyeing processes with natural dyes, compounds, in particular salts, of metals other than alkali metals and alkaline earth metals are often used to improve the adhesion of the natural dye to the keratin fibers. The present dyes and dyeing processes according to the invention can dispense with the use of ions and compounds of metals other than alkali metals and alkaline earth metals.

1. a) Bereitstellung einer wässrigen Färbezusammensetzung (A), die mindestens ein Indigo oder Indirubin produzierendes Pflanzenpulver i), weiterhin Cystein und weiterhin Isatin enthält und einen pH-Wert von 2,0 bis weniger als 10,0, bevorzugt von 4,0 bis 9,0, besonders bevorzugt von 5,0 bis 8,0, außerordentlich bevorzugt von 6,7 bis weniger als 7,5, aufweist, jeweils gemessen bei 20°C,
2. b) Auftragen der wässrigen Färbezusammensetzung (A) auf die Keratinfasern,
3. c) Einwirkenlassen für eine Zeit von 30 Sekunden bis 60 Minuten, bevorzugt 5 bis 45 Minuten, besonders bevorzugt 15 bis 30 Minuten,
4. d) Spülen der Keratinfasern mit Wasser,
5. e) optional Trocknen der Keratinfasern,

wobei in dem Verfahren kein Wasserstoffperoxid eingesetzt wird.Another object of the present invention is a process for the non-oxidative coloring of keratin fibers, in particular human hair, which comprises the following process steps in the order given:

1. a) providing an aqueous dyeing composition (A) which contains at least one indigo or indirubin-producing plant powder i), further cysteine and further isatin and has a pH of 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, each measured at 20°C,
2. b) applying the aqueous dye composition (A) to the keratin fibres,
3. c) Allow to act for a time of 30 seconds to 60 minutes, preferably 5 to 45 minutes, particularly preferably 15 to 30 minutes,
4. d) Rinsing the keratin fibres with water,
5. e) optional drying of the keratin fibres,

No hydrogen peroxide is used in the process.

In process step b), an aqueous dye composition (A) having a pH in the range from 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, each measured at 20°C, is applied to the keratin fibers to be dyed, which are preferably dry.

Surprisingly, it was found that the temporal development of the coloring result on the keratin fibers can be accelerated if the coloring composition (A) is allowed to act with the addition of heat, for example using a heat lamp or a drying hood or a hair dryer. Coloring methods preferred according to the invention are therefore characterized in that the coloring composition (A) is allowed to act with the addition of heat. Coloring methods particularly preferred according to the invention are characterized in that the coloring composition (A) is allowed to act with the addition of heat at a temperature of 25 - 60 °C, particularly preferably at a temperature of 30 - 50 °C, extremely preferably at a temperature of 35 - 40 °C.

With regard to further preferred embodiments of the dyeing processes according to the invention, what has been said about the dyeing agents and dyeing compositions (A) according to the invention applies mutatis mutandis.

In order to preserve the hair-protecting potential of natural dyes, the claimed method is preferably limited to those methods in which the keratin fibers have not been treated with an oxidizing agent in a period of up to 7 days prior to the application of the dye composition (A) according to the invention.

The oxidizing agents that are usually used in hair cosmetics, but which according to the invention are not intended to be used for hair treatment, not even as a pre-treatment, include hydrogen peroxide, persulfates, perbromates, percarbonates, perborates and percarbamides. The oxygen contained in the ambient air does not constitute an oxidizing agent in the context of the invention.

In order to preserve the hair-protecting potential of the natural dyes, preferred methods according to the invention are limited to those methods in which the keratin fibers have not been treated with a keratin-reducing compound in a period of up to 7 days before the application of the dye composition (A) according to the invention.

The keratin fibers are preferably dried after rinsing out the coloring composition (A). Drying can take place without actively applying heat. However, drying can also take place with the addition of heat at a temperature of 25 - 120 °C, particularly preferably at a temperature of 30 - 80 °C, extremely preferably at a temperature of 35 - 60 °C. The heat is preferably applied using a heat lamp, a drying rod, a drying hood, a straightening iron or a hair dryer.

A further feature of the dyeing process according to the invention is that the dye composition (A) is allowed to act on the keratin fibers after application thereto for a time of 30 seconds to 60 minutes, preferably 5 to 45 minutes, particularly preferably 20 to 35 minutes, extremely preferably 25 to 30 minutes.

After the exposure time for the dye composition (A) has elapsed, the keratin fibers are rinsed with water to wash out the dye composition (S).

Optionally, the keratin fibers can be dried after this rinsing step. Drying can be done with an absorbent cloth, such as a towel. The towel-dried hair can optionally be dried partially or completely with a hair dryer or another heat source. It is also possible to let the keratin fibers air dry.

Further dyeing processes preferred according to the invention are characterized in that no oxidation dye precursors are used in them. Typische Oxidationsfarbstoffvorprodukte sind p-Aminophenol, 4-Amino-3-methylphenol, 4-Amino-2-aminomethylphenol, 4-Amino-2-(1,2-dihydroxyethyl)phenol, 4-Amino-2-(diethylaminomethyl)phenol, 2-(2,5-Diaminophenyl)ethanol, 2-(1,2-Dihydroxyethyl)-p-phenylendiamin, N,N-Bis-(2-hydroxyethyl)-p-phenylendiamin, N-(4-Amino-3-methylphenyl)-N-[3-(1H-imidazol-1-yl)propyl]amin, N,N'-Bis-(2-hydroxyethyl)-N,N'-bis-(4-aminophenyl)-1,3-diamino-propan-2-ol, Bis-(2-hydroxy-5-aminophenyl)methan, 1,3-Bis-(2,5-diaminophen-oxy)propan-2-ol, N,N'-Bis-(4-aminophenyl)-1,4-diazacycloheptan, 1,10-Bis-(2,5-diaminophenyl)-1,4,7,10-tetraoxadecan, 2,4,5,6-Tetraaminopyrimidin, 4-Hydroxy-2,5,6-triaminopyrimidin, 2-Hydro-xy-4,5,6-triaminopyrimidin, 2,3-Diamino-6,7-dihydro-1H,5H-pyrazolo-[1 ,2-a]-pyrazol-1-on, 3-Aminophenol, 5-Amino-2-methylphenol, 3-Amino-2-chlor-6-methylphenol, 2-Hydroxy-4-aminophenoxy-ethanol, 5-Amino-4-chlor-2-methylphenol, 5-(2-Hydroxyethyl)-amino-2-methylphenol, 2,4-Dichlor-3-aminophenol, 2-aminophenol, 3-phenylenediamine, 2-(2,4-diaminophenoxy)ethanol, 1,3-bis(2,4-di-aminophenoxy)propane, 1-methoxy-2-amino-4-(2-hydroxyethylamino)benzene, 1,3-bis(2,4-diamino-phenyl)propane, 2,6-bis(2'-hydroxyethylamino)-1- methylbenzene, 2-({3-[(2-Hydroxyethyl)amino]-4-methoxy-5-methylphenyl}amino)ethanol, 2-({3-[(2-Hydroxyethyl)amino]-2-methoxy-5-methylphenyl}amino)ethanol, 2-({3-[(2-Hydroxyethyl)amino]-4,5-dimethylphenyl}amino)ethanol, 2-[3-morpholine- 4-ylphenyl)amino]ethanol, 3-Amino-4-(2-methoxyethoxy)-5-methylphenylamin, 1-Amino-3-bis-(2-hydroxyethyl)aminobenzol, Resorcin, 2-Methylresorcin, 4-Chlorresorcin, 1,2,4-Trihydroxybenzol, 2-Amino-3-hydroxypyridin, 3-Amino-2-methylamino-6-methoxypyridin, 2,6-Dihydroxy-3,4-di-methylpyridin, 3,5-Diamino-2,6-dimethoxypyridin, 1-Phenyl-3-methylpyrazol-5-on, 1-Naphthol, 1,5-Dihydroxynaphthalin, 2,7-Dihydroxynaphthalin, 1,7-Dihydroxynaphthalin, 1,8-Dihydroxynaphthalin, 4-Hydroxyindol, 6-Hydroxyindol, 7-Hydroxyindol, 4-Hydroxyindolin, 6-hydroxyindoline and 7-hydroxyindoline.

The dye compositions (A) according to the invention and preferred according to the invention may optionally contain further additives in order to improve the application properties of these compositions. Preferred additives are in particular thickeners, which ensure that the dye composition (A) remains better on the hair during application.

Coloring compositions (A) used particularly preferably according to the invention contain at least one or more hydrophilic thickeners, which are preferably selected from polysaccharides that can be chemically and/or physically modified. Compounds from the group of polysaccharides are particularly preferred as hydrophilic thickeners according to the invention, since the basic structures of the polysaccharides are of natural origin and biodegradable. Preferred hydrophilic polysaccharide thickeners are selected from celluloses, cellulose ethers of C1-C4 alcohols, cellulose esters, xanthan gum, alginic acids (and their corresponding physiologically acceptable salts, the alginates), agar agar (with the polysaccharide agarose present in agar agar as the main component), starch fractions and starch derivatives such as amylose, amylopectin and dextrins, karaya gum, locust bean gum, gum arabic, pectins, dextrans and guar gum, and mixtures thereof.

Cellulose ethers of C1-C4 alcohols and cellulose esters preferred according to the invention are selected from methylcelluloses, ethylcelluloses, hydroxyalkylcelluloses (such as hydroxyethylcellulose), methylhydroxyalkylcelluloses and carboxymethylcelluloses (such as those with the INCI name Cellulose Gum) and their physiologically acceptable salts.

In preferred embodiments, xanthan gum is included as a hydrophilic thickener with a view to reliably adjusting the viscosity and residue-free application to keratin fibers and the scalp. In further preferred embodiments, carboxymethylcellulose (preferably carboxymethylcellulose with the INCI name Cellulose Gum) is included as a hydrophilic thickener with a view to reliably adjusting the viscosity and residue-free application to keratin fibers and the scalp. In a preferred embodiment, carboxymethylcellulose can be included as the only hydrophilic thickener. A combination of carboxymethylcellulose and hydroxyethylcellulose is particularly preferred.

A combination of carboxymethylcellulose and xanthan (preferably xanthan with the INCI name xanthan gum) may also be preferred according to the invention.

Dyeing compositions (A) which are particularly preferred according to the invention contain at least one hydrophilic thickener in a total amount of from 0.1 to 5% by weight, preferably from 0.5 to 4% by weight, more preferably from 1 to 3.5% by weight and very particularly preferably from 1.2 to 2% by weight, in each case based on the weight of the respective dyeing composition (A).

In a further preferred embodiment of the present invention, the coloring compositions (A) according to the invention contain, in each case based on their weight, 0.1 to 3% by weight, preferably 0.5 to 2.5% by weight, more preferably 1.2 to 2.0% by weight, of xanthan gum.

In a further preferred embodiment of the present invention, the coloring compositions (A) according to the invention contain, in each case based on their weight, 0.1 to 4% by weight, preferably 1 to 2.8% by weight, of carboxymethylcellulose.

In a further preferred embodiment of the present invention, the coloring compositions (A) according to the invention contain, in each case based on their weight, 0.1 to 3% by weight, preferably 0.5 to 2.5% by weight, more preferably 1.2 to 2.0% by weight, of hydroxyethylcellulose.

Particularly preferred dye compositions (A) according to the invention contain at least one organic solvent which has a phenyl group in the molecule. This solvent is preferably selected from phenoxyethanol, benzyl alcohol and mixtures thereof. Surprisingly, it has been found that such aromatic solvents can have a positive effect on the dyeing results of the dyeing process according to the invention; this was observed in particular when the dye composition (A) contains such an aromatic solvent.

In a further preferred embodiment of the present invention, the dye compositions (A) preferred according to the invention contain, in each case based on their weight, 0.1 to 3% by weight, preferably 0.5 to 2.5% by weight, more preferably 0.8 to 1.0% by weight, of at least one organic solvent which has a phenyl group in the molecule. In a further preferred embodiment of the present invention, the dye compositions (A) according to the invention contain, in each case based on their Weight, 0.1 to 3 wt.%, preferably 0.5 to 2.5 wt.%, more preferably 0.8 to 1.0 wt.%, of at least one organic solvent selected from phenoxyethanol, benzyl alcohol and mixtures thereof.

Particularly preferred dye compositions (A) according to the invention are characterized in that they contain at least one aliphatic solvent selected from C ₁ -C ₄ alkanols and C ₂ -C ₄ polyols, in particular selected from ethanol, isopropanol, n-propanol, ethylene glycol, 1,2-propanediol, glycerin and 1,3-butylene glycol, and mixtures of these solvents, but only in a total amount of 0.01 - 8 wt.%, preferably 0.1 - 6 wt.%, particularly preferably 0.5 - 4 wt.%, in each case based on the weight of the dye composition (A).

Other dyeing compositions (A) which are particularly preferred according to the invention are characterized in that they do not contain an aliphatic solvent selected from C ₁ -C ₄ alkanols and C ₂ -C ₄ polyols.

In order to make the coloring compositions (A) according to the invention also sensorially attractive for the user, further coloring compositions (A) which are particularly preferred according to the invention are characterized in that they contain at least one perfume oil which contains at least one fragrance compound or odoriferous compound.

Dyeing compositions (A) which are particularly preferred according to the invention are characterized in that they contain at least one fragrance in a total amount of 0.01-5% by weight, preferably 0.1-3% by weight, particularly preferably 0.5-2% by weight, extremely preferably 1-1.5% by weight, in each case based on the weight of the dyeing composition (A).

Examples of implementation

The embodiments presented below are intended to explain the subject matter of the invention in more detail without limiting it thereto.

As an example of the invention, the following dye composition (A) according to the invention was prepared: Table 1: Dye composition according to the invention (A-1) ground leaves of Indigofera tinctoria L.* 2.50 grams (R)-(+)-Cysteine (L-Cysteine) 0.50 grams Isatin 0.05 grams Water, demineralized 46.95 grams pH value (20°C) 7.4 * powdered leaves of Indigofera tinctoria, pH of the 5 wt.% dispersion in water: 6.8 to 7.2 (20°C)

2.5 g of indigo powder were dispersed in 46.95 grams of demineralized water and 0.5 g of L-cysteine and 0.05 g of isatin were added and dissolved. This dispersion was heated to approx. 37 °C ± 1 °C on a stir plate while stirring. When this temperature was reached, a strand of buffalo belly hair (tied in a round shape, approx. 8 cm of free hair) was placed in this dispersion (dye composition (A-1)) for 30 minutes and stirred.

The liquor ratio, i.e. the weight of dye per gram of hair, was 50 g of dye per 1 g of hair (50:1).

After completion of the dyeing process, the hair strands were rinsed under running deionized water for 30 seconds and combed 20 times (20°C).

The hair strands were then dried with a commercially available hair dryer at a defined distance (d = 10 cm) and a defined temperature (T = 80 ± 5 °C) by combing them 20 times.

Determination of staining results using spectrophotometric measurements

All colorimetric measurements were carried out using the Spectraflash SF 600 colorimetric device from Datacolor.

The color difference, also known as dE or ΔE, can be easily determined colorimetrically using a colorimeter that measures colors in the L*, a*, b* color space, for example a Datacolor colorimeter, type Spectraflash SF 600.

The L*, a*, b* color space refers to the CIELAB color space. The L value represents the brightness of the color (black-white axis); the higher the L value, the brighter the color. The a value represents the red-green axis of the system; the higher this value, the more the color is shifted towards red. The b value represents the yellow-blue axis of the system; the higher this value, the more the color is shifted towards yellow.

The color shift ΔE, i.e. the color difference between two (hair) colors, for each of which an L*, a*, b* value combination was determined, is calculated according to the following formula: $$\mathrm{\Delta }\text{E}={\left(\mathrm{\Delta }{\text{L}}^2+\mathrm{\Delta }{\text{a}}^2+\mathrm{\Delta }{\text{b}}^2\right)}^{0.5}$$

The larger the value of ΔE, the more pronounced the color difference.

A D65 illuminant and diffuse/8° optical configuration were used for the spectrophotometer measurements. Spectral reflectance data for each sample from 380 nm to 700 nm were converted to colorimetric data using DCI Color software. Reflectance measurements were determined for each hair sample, with the average of 4 measurements recorded.

mit

• Lv, av, bv: Farbmetrikwerte für gefärbte Strähne
• Ln, an, bn: Farbmetrikwerte für ungefärbte Strähne

The colour difference (ΔE) between undyed strand and dyed strand (with indigo/cysteine/isatin or with indigo alone) was calculated according to the following formula: $$\mathrm{\Delta }E=\sqrt{{\left(Lv-Ln\right)}^2+{\left(av-an\right)}^2+{\left(bv-bn\right)}^2},$$

with

• Lv, av, bv: colorimetric values for colored strands
• Ln, an, bn: colorimetric values for undyed strand

In order to also track the temporal development of the final color, measurements were taken on day 0 directly after coloring and 14 days after coloring and compared with each other.

Table 2: L*, a*, b*, ΔE values of indigo staining with cysteine/isatin and indigo alone

The differences between the control strand and the strands with addition of cysteine/isatin immediately after staining at 37 °C (day 0) and 14 days after staining are shown below (mean values). BatchName CIE L pattern CIE a pattern CIE b pattern Day 0 Indigo without cysteine/isatin (control) mean 45.4 -13.0 -6.8 Indigo + Cysteine + Isatin (37°C) Average 36.6 27.0 -7.4 Difference between control and cysteine/isatin strand: ΔE = 40.9 Day 14 Indigo without cysteine/isatin (control) mean 36.0 1.4 -13.6 Indigo + Cysteine + Isatin (37°C) Average 34.8 30.5 -8.0 Difference between control and cysteine strand/isatin: ΔE = 26.3

The addition of cysteine and isatin to the dispersion of Indigofera tinctoria leaf powder results in an intense magenta tone rather than a blue-turquoise tone being visible on the hair fiber after coloring (see Table 2). The change in the color tone of this strand in the two weeks after coloring becomes even more uniform overall, but is negligible (ΔE of approximately 1 to 3).

In the coloring according to the invention described above, in contrast to the control, the magenta tone can be observed on the hair strand directly after the treatment.

Influence of dyeing temperature

The same coloring, but carried out at 20°C, shows a pink tint directly after the treatment. This could not be quantified due to the remaining moisture. However, an irregular, stronger red-magenta tone develops during the subsequent blow-drying (temperature at 5 cm distance from the blow-dryer: 96 °C, at 15 cm distance from the blow-dryer: 79 °C). The color difference between coloring at 37 °C followed by blow-drying and coloring at 20 °C followed by blow-drying was ΔE = 12.7.

Table 3: L*, a*, b*, ΔE values of indigo staining with cysteine/isatin and indigo alone, staining at 20°C and blow-drying

The differences between the control strand and the strands with addition of cysteine/isatin immediately after staining at 20 °C (day 0) after staining are shown below (mean values). BatchName CIE L pattern CIE a pattern CIE b pattern Day 0 Indigo without cysteine/isatin (control) mean 45.4 -13.0 -6.8 Indigo + Cysteine + Isatin (20°C) Average 47.1 21.7 -2.6 Difference between control and cysteine/isatin strand (staining at 20°C): ΔE = 12.7

Influence of the pH value of the dye on the color result

The following shows how the pH value of the dye dispersion affects the color result.

The dyes are produced and the strands are dyed using the process described above. In the dispersion (A-1) of indigo leaves, 1% by weight cysteine and 0.1% by weight isatin in water, a pH of 7.4 is spontaneously established. The pH of other dye dispersions according to the invention was adjusted to 3, 5, 8 and 10 with sodium hydroxide solution or hydrochloric acid, each measured at 20°C. The dyeing was carried out at 37°C. After dyeing, all strands were washed out and dried according to the usual protocol (see above). The color results were compared with those achieved at the "spontaneous" pH of 7.4. The dye dispersion with pH 10 is not according to the invention (V-1). Table 4: L*, a*, b*, ΔE values of indigo staining with cysteine and isatin at 37 °C and different pH values directly after staining (day 0) Indigo staining with cysteine + isatin at 37 °C, day 0 pH spontaneous (7.4) pH 3 (A-2) pH 5 (A-3) pH8 (A-4) pH 10 (V-1) 36.6 27.0 -7.4 40.6 24.7 -4.0 34.0 29.6 -4.8 34.2 25.2 -7.1 65.3 7.7 10.8 Difference to pHspontan: ΔE = 5.8 ΔE = 4.5 ΔE = 2.9 ΔE = 39.1

It can be observed that the colour intensity and the magenta tone increase at pH 5. The result of the colouring dispersion at pH 3 loses darkness (intensity) and redness with a ΔE of 5.8 compared to the dispersion with the spontaneous pH of 7.4. At pH 8, only the darkness (intensity) increases - the a* value, which represents the red intensity, decreases slightly compared to the strand dyed at pH 7.4. At pH 10 (not according to the invention) the desired color is not visible on the hair fiber.

The data presented lead to the conclusion that indigo in combination with cysteine and isatin in the color dispersion at pH 5 produces the darkest, most intense and most red result. The color dispersion in the slightly alkaline range (pH 8) comes closest to the color result with the spontaneous pH value (7.4) (ΔE = 2.9). At a pH of 10 of the dispersion, no color result comparable to the spontaneously occurring pH value of 7.4 is achieved.

Comparison of the colorants according to the invention with the teaching of DE4211450A1

The difference between a DE4211450A1 known dyes containing isatin and cysteine and a dye according to the invention containing indigo plant leaves, isatin and cysteine will be illustrated by the following series of measurements. To produce the comparative dye according to DE4211450A1 0.5 g of (R)-(+)-cysteine (1 wt% of the total solution) and 0.05 g of isatin (0.1 wt% of the total solution) were dissolved in 49.45 grams of demineralized water.

Test series A: This solution was then heated to 37 °C, a strand of hair was placed in the solution for 30 minutes and stirred constantly at 37 °C ± 1 °C (liquor ratio: 50 ml for 1 g strand of hair; pH: approx. 6.7, measured at 20 °C).

Test series B: A strand of hair was placed in another previously described, unheated cysteine-isatin solution for 30 minutes and stirred constantly at 20 °C (liquor ratio: 50 ml for 1 g strand of hair; pH: approx. 6.7, measured at 20 °C).

After dyeing procedures A or B, the solution was washed off the strand (30 seconds under running deionized water, twenty combings at 20°C) and the strand was dried (hair dryer, distance d = 10 cm, temperature: T = 80 ± 5 °C, twenty combings).

The result is compared with the color result of the strand treated with the dye A-1 according to the invention at 37 °C or at 20 °C, see Tables 5 and 6. Table 5: Comparison between treatment according to the invention with indigo and cysteine and isatin at 37 °C and non-inventive treatment with cysteine and isatin at 37 °C directly after rinsing and blow-drying (the L*, a*, b* values are shown) Indigo staining with cysteine + isatin at 37 °C Cysteine + Isatin in water at 37 °C 36.6 27.0 -7.4 59.4 17.8 19.8 Difference: ΔE = 36.3

The non-inventive treatment of the strand results in a coloration with a significantly lighter shade (higher L* value) that tends less towards red and more towards yellow (ΔE = 36.3). Table 6: Comparison between the inventive treatment with indigo and cysteine and isatin at 20 °C and the non-inventive treatment with cysteine and isatin at 20 °C immediately after rinsing and blow-drying (the L*, a*, b* values are shown) Indigo staining with cysteine + isatin at 20°C Cysteine + Isatin in water at 20°C 47.1 21.7 -2.6 69.9 4.1 14.7 Difference: ΔE = 33.6

The treatment of the strand not according to the invention results in a colouring with a significantly lighter shade (higher L* value) which tends less towards the reddish-magenta direction (ΔE = 33.6).

Influence of the reducing agent

The following shows how replacing cysteine with another reducing agent affects the color result.

The dyes were produced and the strands were dyed using the process described above. In addition to the dispersion (A-1) according to the invention made from 5% by weight of indigo leaves, 1% by weight of cysteine and 0.1% by weight of isatin in water, a comparison dispersion (V-2) made from 5% by weight of indigo leaves, 1% by weight of ascorbic acid and 0.1% by weight of isatin in water was produced. One batch was dyed on strands of hair at 20°C and another batch at 37°C. Both strands were then washed out and dried according to the usual protocol (see above). The pH value of the dispersion with indigo, ascorbic acid and isatin was 5.0 (measured at 20°C) spontaneously, i.e. without the addition of further pH adjusters. The color results achieved are summarized in Table 7 and Table 8. Table 7: Comparison between treatment according to the invention with indigo and cysteine and isatin at 37 °C and non-inventive treatment with indigo and ascorbic acid and isatin at 37 °C immediately after rinsing and blow-drying (L*, a*, b* values are shown) Color result according to the invention (day 0) Non-inventive color result (day 0) 36.6 27.0 -7.4 39.60 24.35 -0.32 Difference: ΔE = 8.1

The use of ascorbic acid instead of cysteine results in a slightly less dark, red and more blue result when dyeing at 37 °C. The two color results differ from each other by ΔE = 8.1. Table 8: Comparison between treatment according to the invention with indigo and cysteine and isatin at 20 °C and non-inventive treatment with indigo and ascorbic acid and isatin at 20 °C immediately after rinsing and blow-drying (the L*, a*, b* values are shown) Indigo staining with cysteine + isatin at 20°C Indigo dyeing with ascorbic acid + isatin at 20°C Day 0 47.1 21.7 -2.6 58.03 13.33 11.38 Difference: ΔE = 19.6

The difference between the color results according to the invention and those not according to the invention is greater when dyed at 20°C than when dyed at 37°C: ΔE = 19.6 instead of 8.1. The strand treated with ascorbic acid (not according to the invention) is significantly lighter, less red and more yellow than the strand dyed according to the invention.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2015082482 A1 [0006]
• DE 4211450 A1 [0008, 0101]

Claims (15)

Agent for the non-oxidative coloration of keratin fibers, in particular human hair, containing water, cysteine, isatin and at least one indigo or indirubin producing plant powder i), wherein the agent has a pH of 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, in each case measured at 20°C. Agent for non-oxidative staining according to Claim 1 , characterized in that cysteine is contained in molar excess to isatin. Agent for non-oxidative staining according to Claim 2 or 3 , characterized in that the indigo or indirubin producing plant(s) is/are selected from at least one species of the following genera: - Indigofera, in particular Indigofera tinctoria, Indigo suffruticosa, Indigofera articulata, Indigofera arrecta, Indigofera heterantha 'Gerardiana', Indigofera argentea or Indigofera longiracemosa; - Isatis, in particular Isatis tinctoria (woad); - Persicaria, in particular Persicaria tinctoria (dyer's knotweed); - Wrightia, in particular Wrightia tinctoria; - Calanthe, in particular Calanthe veratrifolia; and - Baphicacanthus cusia, synonym Strobilanthes cusia, wherein the indigo or indirubin producing plant(s) is/are preferably selected from the genus Indigofera and in particular from Indigofera tinctoria. Remedy according to one of the Claims 1 - 3 , characterized in that the powder of the indigo or indirubin producing plant consists, based on its weight, of at least 50 wt. %, preferably at least 80 wt. %, particularly preferably more than 80 - 100 wt. %, of the leaves of the plant. Remedy according to one of the Claims 1 until 4 , characterized in that the powder of the indigo or indirubin producing plant contains indican in an amount of 2 - 5 wt.%, preferably 2.5 - 4.5 wt.%, particularly preferably 3 - 4.1 wt.%, based on the weight of the powder. Remedy according to one of the Claims 1 - 5 , characterized in that at least one indigo or indirubin producing plant powder i) is contained in a total amount of 1 - 80 wt.%, preferably 2 - 50 wt.%, particularly preferably 3 - 25 wt.%, extremely preferably 4 - 15 wt.%, further extremely preferably 5 - 10 wt.%, further extremely preferably 6 - 7 wt.%, based on the weight of the agent. Remedy according to one of the Claims 1 - 6 , characterized in that powdered leaves of Indigofera tinctoria are contained in an amount of 1 - 80 wt.%, preferably 2 - 50 wt.%, particularly preferably 3 - 25 wt.%, extremely preferably 4 - 15 wt.%, further extremely preferably 5 - 10 wt.%, further extremely preferably 6 - 7 wt.%, based on the weight of the agent. Remedy according to one of the Claims 1 - 7 , characterized in that cysteine is contained in an amount of 0.1 - 5.0 wt.%, preferably 0.5 - 3.0 wt.%, particularly preferably 0.8 - 2.0 wt.%, extremely preferably 1.0 - 1.5 wt.%, based on the weight of the agent. Remedy according to one of the Claims 1 - 8 , characterized in that isatin is contained in an amount of 0.01 - 1.0 wt.%, preferably 0.05 - 0.5 wt.%, particularly preferably 0.08 - 0.3 wt.%, extremely preferably 0.1 - 0.2 wt.%, based on the weight of the agent. Remedy according to one of the Claims 1 - 9 , characterized in that water is contained in an amount of 19.9 - 95.0 wt.%, preferably 30.0 - 90.0 wt.%, particularly preferably 50.0 - 88.0 wt.%, extremely preferably 60.0 - 85.0 wt.%, based on the weight of the agent. Remedy according to one of the Claims 1 - 10 , characterized in that it does not contain hydrogen peroxide. Remedy according to one of the Claims 1 - 11 , characterized in that the molar ratio of cysteine to isatin is 1.5 to 20, preferably 3 to 18, particularly preferably 5 to 15, extremely preferably 10 to 13. Process for the non-oxidative coloring of keratin fibers, in particular human hair, which comprises the following process steps in the order given: a) providing an aqueous coloring composition (A) which contains at least one indigo or indirubin-producing plant powder i), furthermore cysteine and isatin and has a pH value of 2.0 to less than 10.0, preferably from 4.0 to 9.0, particularly preferably from 5.0 to 8.0, extremely preferably from 6.7 to less than 7.5, each measured at 20°C, b) applying the aqueous coloring composition (A) to the keratin fibers, c) allowing to act for a time of 30 seconds to 60 minutes, preferably 5 to 45 minutes, particularly preferably 15 to 30 minutes, d) rinsing the keratin fibers with water, e) optionally drying the keratin fibers, wherein no hydrogen peroxide is used in the process. Dyeing process according to Claim 13 , characterized in that the dyeing composition (A) is allowed to act with the addition of heat, preferably at a temperature of 25 - 60 °C, particularly preferably at a temperature of 30 - 50 °C, extremely preferably at a temperature of 35 - 40 °C. Dyeing process according to one of the Claims 13 or 14 , characterized in that the dyeing composition (A) comprises an agent according to one of the Claims 2 - 12 is.